Amplifier is bigger sound generally gets louder as for better that's a matter of opinion. A lot of people would prefer a small tube amp over a large solid state and jimmy page even recorded a few zep songs in the studio using very small amps cause he preferred their tones for said songs over a lot of the bigger amps available at the time.

Quality is relatively objective, it's all a matter of what you prefer.

You need to efficiently utilize the power of your amp. This is very similar to finding the best horsepower band for your car. For example, my car has low hp in the 1k to 3 or 4k bands. But high hp in the 4 and up k bands.

i.e.

If you have a 100 watt amp and set the volume to 1, you will not be getting the 'best' (and it's all subjective) tones from you amp, and you'll essentailly be wasting yours amps ability. But if you have a 50 watt amp and set the volume to 5 or 6 (or even higer) you will be better utilizing your amps power and therefore you will have a more versitile amp. It's like volume swelling vs volume dampening.

In other words... Don't get an amp you aren't going to crank up! It would be like buying a Ferrari just to idle around the block. Use your money wisely to get the most bang for your buck, but not more bang than you are willing to use.

@Guitarslinger124 Good explanation dude. I used a 160 watt amp in church but since I never play loud, I just use it for personal monitor, it did not sound good. I backed off to a 40 watt and got a better sound since I was able to push 60-75 of the amp.